The present invention relates to a method and apparatus for operating inductive magnetic write heads for use in magnetic storage devices, such as magnetic disk drives, tape drives and the like.
A typical system for writing data to a magnetic medium employs an inductive write head having a high permeability magnetic core. The core has a nonmagnetic gap that creates a stray magnetic field in response to a current flowing through the write head, with the magnetic field ultimately writing the data. A sufficient writing field must be applied to the magnetic medium in order to record data. Specifically, the magnetic field strength of the stray field emanating from the gap must at least exceed the coercivity of the magnetic medium in order for data to be recorded. It is common in the industry to refer to the fringing field as contour lines of equal strength. The terms xe2x80x9cbubblexe2x80x9d or xe2x80x9cwrite bubblexe2x80x9d are used to represent the contour line of field strength equal to the coercivity of the medium. The strength of the stray field inside the write bubble is greater than the coercive field of the magnetic medium. Likewise, the strength of the stray field outside of the bubble, and therefore further from the gap, is less than the coercivity of the magnetic medium.
As the magnetic medium passes adjacent the gap, the magnetic field from the head magnetizes the medium in a selected direction based on the direction of the magnetic field, and hence the direction of current in the coil. The magnetization remains in the orientation established by the magnetic field after the magnetic field has been removed, so the magnetic pattern recorded in the medium can later be xe2x80x9creadxe2x80x9d by another magnetic read head. As explained above, the magnetic field from the gap includes a region in which the magnetic field exceeds the coercivity of the medium, which is known as the magnetic xe2x80x9cbubblexe2x80x9d or xe2x80x9cwrite bubblexe2x80x9d utilized to encode a desired magnetic pattern on the medium. The magnetization of the medium within the bubble is oriented to the direction of the field within the write bubble. As the magnetic medium moves relative to the head, the magnetic field from the head continues to orient the magnetization of the medium as it passes through the bubble. Thus, with reference to FIGS. 1 and 2, magnetic head 10 includes an inductive write element including magnetic core 12 with coil 14 winding around magnet 12 to carry the field-generating current. Opposite poles of magnetic core 12 confront one another across gap 16. Magnetic sensor 18 for reading the written data is located adjacent to the inductive write element, with magnetic shield 20 adjacent to sensor 18, thereby providing functionality of a read/write head. Application of a current through coil 14 generates a magnetic field at the air bearing surface 24 of the head, which extends into magnetic medium 26. The magnetic field within bubble 22 is strong enough to orient the magnetization of medium 26 based on the direction of current in coil 14 of head 10, while the magnetic field outside of bubble 22 is not strong enough to orient the magnetization of medium 26. The region within medium 26 in which the magnetization is oriented comprises the region bounded by dimensions L0 and R0, at the forward and trailing edges of influence of bubble 22. As medium 26 moves in the direction indicated by arrow v, bubble 22 writes along the track to a position bounded by positions L1 and R1. Hence, the magnetization orientation due to current in coil 14 of head 10 after successive time increments encompasses the region between L0 and R1.
A single bit cell may be quite smaller than the region between L0 and R1, and may encompass only that portion of the region between L0 and L1. Consequently, if a current reversal in coil 14 of head 10 causes a reversal of a magnetic field when medium 26 is in the position illustrated in FIG. 2, bubble 22 orients the dipoles oppositely, thereby reorienting the dipoles in the region between L1 and R1 and overwriting that portion of the medium between L1 and R0 that had been written when medium 26 was in the position illustrated in FIG. 1. In this manner, data are written with bit cells in the medium smaller than the bubble, specifically having a spatial extent bounded by L0 and L1.
Most magnetic disk drive systems store data by defining each magnetic transition in the medium as a binary xe2x80x9c1xe2x80x9d and the lack of a transition as a binary xe2x80x9c0xe2x80x9d. Clock recovery techniques recover clock information from the frequency of data recorded on the media. These circuits rely on the presence of frequent transitions (binary 1s) in order to synchronize to the data. Consequently, run length limited codes are employed to ensure that long streams of binary 0s do not occur. Most magnetic disk drives employ run length limited codes limiting the number of consecutive binary 0s to a number between six and twelve.
Most writer circuits for writing data via magnetic write heads operate on the principle of reversing the direction of current in the coil of the head and maintaining a reasonably steady state current level until the next transition. Thus, as illustrated in FIG. 3, a transition at time TO, representing a binary 1, reverses the direction of current through the coil from positive to negative between steady state levels of +IW and xe2x88x92IW. The current remains at a steady state level of xe2x88x92IW until time T5, representing four consecutive binary 0s, when the current is again reversed to +IW, representing another binary 1. (FIG. 3 shows a peak or spike in the current at the transitions, caused by current overshoot that is often generated to help decrease the current and magnetic field reversal time in the head.)
The present invention is directed to a pulse-mode writer that modifies the write current waveform to change the steady state current conditions of the write driver circuit, and instead employs pulses to record transitions and takes advantage of the enlarged size of the magnetic bubble to record the lack of transitions that signify binary 0s.
The present invention is a pulse-mode data writing protocol which reduces the time required to implement a transition in the direction of magnetization of a recording medium, and which reduces the total power required to encode a given data sequence. After a magnetic transition is encoded on the medium by generating a write current pulse through the write head, the write current through the recording head is reduced, thereby utilizing the spatial extent of the write bubble to encode the lack of a transition on the medium. Alternate configurations of the present invention may be implemented for various scenarios of write bubble size versus maximum cell size, with each configuration utilizing the principle of the invention to reduce the write current at some point between magnetic transitions to reduce the power and transition time of the system.